Collapsible catheter and method for calculating fractional flow reserve

ABSTRACT

A catheter for measuring a fractional flow reserve includes a proximal shaft, a distal shaft coupled to the proximal shaft, a pressure sensor coupled to the distal shaft, and at least one pressure sensor wire operably connected to the pressure sensor. The proximal shaft includes a radially expanded configuration and a radially collapsed configuration, wherein the proximal shaft has a first outer diameter in the radially expanded configuration and a second outer diameter smaller than the first outer diameter in the radially collapsed configuration. The distal shaft defines a guidewire lumen configured to receive a guidewire therein.

FIELD OF THE INVENTION

The present invention relates to systems and methods for calculating aFractional Flow Reserve. More particularly, the present inventionrelates to a collapsible catheter for calculating a Fractional FlowReserve.

BACKGROUND OF THE INVENTION

The severity of a stenosis or lesion in a blood vessel may be assessedby obtaining proximal and distal pressure measurements relative to thegiven stenosis and using those measurements for calculating a value of aFractional Flow Reserve (FFR). FFR is defined as the ratio of a distalpressure P_(d) measures on a distal side of the stenosis to a proximalpressure P_(a) measured on a proximal side of the stenosis, typicallywithin the aorta (FFR=P_(d)/P_(a)). Conventionally, a sensor is placedon a distal portion of a guidewire (FFR wire) to obtain/measure thedistal pressure P_(d), while an external pressure transducer is fluidlyconnected via tubing to a guide catheter for obtaining the proximal, oraortic (AO) pressure P_(a). Once the guide catheter is positioned insitu, and the pressure of the blood filling the lumen of the guidecatheter is equal to the pressure of the blood at the distal tip of theguide catheter, tubing that fluidly connects the proximal end of theguide catheter to the external pressure transducer also fills with bloodsuch that the external pressure transducer measures the pressure of theblood at the distal tip of the guide catheter. The FFR wire is advancedthrough the guide catheter and through the lesion to a distal side ofthe lesion. The sensor on the FFR wire measures the distal pressure.

Calculation of the FFR value provides a stenosis specific index of thefunctional severity of the stenosis in order to determine whether theblockage limits blood flow within the vessel to an extent that treatmentis needed. An optimal or normal value of FFR in a healthy vessel is1.00, while values less than about 0.80 are generally deemed significantand in need of an interventional treatment. Common interventionaltreatment options include balloon angioplasty and/or stent implantation.If an interventional treatment is required, the interventional device,such as a balloon catheter, is tracked over a guidewire to the site ofthe stenosis. Conventional FFR wires generally are not desired byclinicians to be used as guidewires for such interventional devices.Accordingly, if an interventional treatment is required, the cliniciangenerally removes the FFR wire, inserts a conventional guidewire, andtracks the interventional device to the treatment site over theconventional guidewire.

To address this concern, efforts have been made to utilize catheters totake pressure measurements for calculating FFR. Using a catheter (FFRcatheter or micro-catheter), a clinician may use a preferred guidewirefor tracking the FFR catheter to the site of the stenosis. If aninterventional treatment is required, the FFR catheter may be removedwhile the guidewire used with the FFR catheter may remain in situ, andthe interventional device may be tracked over the existing guidewire tothe site of the stenosis.

However, such FFR catheters are generally larger in cross-sectionalprofile than FFR wires. Therefore, some error may be introduced into themeasured proximal pressure P_(a) and the measured distal pressure P_(d),as compared to measurements taken using an FFR wire. In particular, anFFR catheter disposed over a guidewire occupies a larger percentage ofthe guide catheter lumen than a comparatively smaller profile FFR wire.Occupying a larger percentage of the guide catheter lumen may affect theaccuracy of the measured proximal pressure P_(a), which, as explainedabove, is based on blood filling the lumen of the guide catheter. Thiserror is referred to as dampening of the AO pressure wave. Due to thereduced space between the inner surface of the guide catheter and anouter surface of the proximal portion of the FFR catheter/guidewirecombination, the pressure at the distal end of the guide catheter doesnot propagate proximally through the guide catheter such that changes inthe pressure at the distal end of the guide catheter are not properlymeasured by the external pressure transducer. Thus, using a largerprofile FFR catheter may introduce errors in the measured proximalpressure (P_(a)). Such errors would then be transferred to thecalculation of FFR, which is based in part on the measured proximalpressure.

Further, the lager cross-sectional profile of a distal portion of an FFRcatheter, as compared to an FFR wire, occupies a larger percentage ofthe vessel distal of the guide catheter and across the stenosis.Occupying a larger percentage of the vessel affects the fluid dynamicsof the blood flow through the stenosis, thereby causing the measureddistal pressure P_(d) to deviate from distal pressure of the same vesseland same stenosis measured with a conventional FFR wire. Deviation ofthe measured distal pressure P_(d) is transferred to the calculated FFR.

Thus, using an FFR catheter may cause the calculated FFR to deviate fromFFR calculated using measurements taken with an FFR wire. Becauseinterventional decisions have been made based on FFR measured using FFRwires, this may lead to “false positives” or “false negatives”. A “falsepositive” is where the FFR calculated using measurements taken with anFFR catheter is lower than the threshold for intervention (e.g. below0.80) but if the FFR were calculated using measurements taken with anFFR wire, the FFR would have been higher than the threshold (e.g. above0.80). A “false negative” is where the FFR calculated using measurementstaken with an FFR catheter is higher than the threshold for intervention(e.g. above 0.80) but if the FFR were calculated using measurementstaken with an FFR wire, the FFR would have been lower than the threshold(e.g. below 0.80).

Accordingly, there is a need to reduce the cross-sectional profile ofFFR catheters to minimize deviation of FFR calculated using an FFRcatheter as compared to FFR calculated using an FFR guidewire.

BRIEF SUMMARY OF THE INVENTION

Embodiments hereof relate to a catheter for measuring a fractional flowreserve including a proximal shaft, a distal shaft, a pressure sensor,and at least one pressure sensor wire. The proximal shaft includes aradially expanded configuration and a radially collapsed configuration.The proximal shaft has a first outer diameter in the radially expandedconfiguration and a second outer diameter in the radially collapsedconfiguration. The distal shaft defines a guidewire lumen configured toreceive a guidewire. The pressure sensor is coupled to the distal shaft.The at least one pressure sensor wire is operably connected to thepressure sensor and extends proximally from the pressure sensor within adistal shaft wall of the distal shaft and into a proximal shaft wall ofproximal shaft.

Embodiments hereof also relate to a catheter for measuring a fractionalflow reserve including a proximal shaft, a distal shaft coupled to theproximal shaft, a pressure sensor coupled to the distal shaft, at leastone pressure sensor wire, and a movable shaft. The distal shaft iscoupled to the proximal shaft. The distal shaft defines a guidewirelumen configured to receive a guidewire. The at least one pressuresensor wire is operably connected to the pressure sensor and extendsproximally from the pressure sensor within the distal shaft proximallythrough the proximal shaft. The movable shaft includes a lumen sized toreceive the proximal shaft. The catheter includes a first configurationwith the movable shaft disposed over the proximal shaft and a secondconfiguration with the movable shaft removed from the proximal shaft.

Embodiments hereof also related to a method for calculating a FractionalFlow Reserve in a vessel. The method includes delivering a catheter to atreatment site in the vessel. The catheter includes a pressure sensorcoupled to a distal shaft, a proximal shaft, and a stiffening shaftdisposed within an expansion lumen of the proximal shaft. The catheteris delivered to the treatment site with the stiffening shaft disposed inthe expansion lumen and such that the pressure sensor is located on adistal side of a stenosis of the vessel. The method further includesremoving the stiffening shaft from the expansion lumen such that theproximal shaft collapses from a radially expanded configuration to aradially collapsed configuration. The method further includes measuringa distal pressure distal of the stenosis using the pressure sensor andmeasuring a proximal pressure on a proximal side of the stenosis. Theproximal pressure is measured with the proximal shaft in the radiallycollapsed configuration. The method further includes calculating theFractional Flow Reserve using the measured distal pressure and themeasured proximal pressure.

Embodiments hereof also relate to a method for calculating a FractionalFlow Reserve in a vessel. The method includes delivering a catheter to atreatment site in the vessel. The catheter includes a pressure sensorcoupled to a distal shaft, a proximal shaft, and a movable shaftslidingly disposed around an outer surface of the proximal shaft. Thecatheter is delivered to the treatment site with the movable shaftdisposed around the proximal shaft and such that the pressure sensor islocated on a distal side of a stenosis of the vessel. The method furtherincludes removing the movable shaft from around the proximal shaft. Themethod further includes measuring a distal pressure distal of thestenosis using the pressure sensor and measuring a proximal pressure ona proximal side of the stenosis. The proximal pressure is measured withthe movable shaft removed from the proximal shaft. The method furtherincludes calculating the Fractional Flow Reserve using the measureddistal pressure and the measured proximal pressure.

Embodiments hereof also relate to a catheter for measuring a fractionalflow reserve including a proximal shaft, a distal shaft coupled to theproximal shaft, a pressure sensor coupled to the distal shaft, and atleast one pressure sensor wire operably connected to the pressuresensor. The proximal shaft includes a distal portion configured toextend through a stenosis in a vessel. The distal portion of theproximal shaft includes a radially expanded configuration having a firstdiameter and a radially collapsed configuration having a seconddiameter, wherein the first diameter is larger than the second diameter.The distal shaft includes a guidewire lumen configured to receive aguidewire therein. The at least one pressure sensor wire extendsproximally from the pressure sensor through the distal shaft.

Embodiments hereof are also directed to a catheter for measuring afractional flow reserve include a proximal shaft, a distal shaft coupledto the proximal shaft, a pressure sensor coupled to the distal shaft,and at least one pressure sensor wire operably connected to the pressuresensor. The distal shaft includes a distal portion and a collapsibleportion proximal of the distal portion. The collapsible portion includesa radially expanded configuration having a first diameter and a radiallycollapsed configuration having a second diameter, wherein the firstdiameter is larger than the second diameter. A guidewire lumen extendsthrough the collapsible portion and the distal portion of the distalshaft. The guidewire lumen is configured to receive a guidewire therein.The collapsible portion is in the radially expanded configuration with aguidewire disposed in the guidewire lumen of the collapsible portion,and the collapsible portion is in the radially collapsed configurationwhen the guidewire is removed from the guidewire lumen of thecollapsible portion.

Embodiments hereof are also direct to method for calculating aFractional Flow Reserve in a vessel. The method includes delivering acatheter to a treatment site in the vessel. The catheter includes apressure sensor coupled to a distal portion of the catheter. Thecatheter is delivered to the treatment site such that the pressuresensor is located on a distal side of a stenosis of the vessel and aradially expandable portion of the catheter is disposed through thestenosis. The catheter is delivered to the treatment site with theradially expandable portion in a radially expanded configuration havinga first diameter. The method further includes collapsing the radiallyexpandable portion to a radially collapsed configuration having a seconddiameter smaller than the first diameter. The method further includesmeasuring a distal pressure distal of the stenosis using the pressuresensor. The distal pressure is measured with the radially expandableportion in the radially collapsed configuration. The method furtherincludes measuring a proximal pressure proximal of the stenosis. Themethod further includes calculating the Fractional Flow Reserve usingthe measured distal pressure and the measured proximal pressure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side illustration of a catheter for calculating a FractionalFlow Reserve (FFR) in accordance with an embodiment hereof, with aproximal shaft in a radially expanded configuration.

FIG. 2 is a side illustration of the catheter of FIG. 1 with theproximal shaft in a radially collapsed configuration.

FIG. 3A is a cross-sectional illustration of an embodiment of theproximal shaft of the catheter of FIG. 1, taken along line 3A-3A of FIG.1.

FIG. 3B is a cross-sectional illustration of an embodiment of theproximal shaft of the catheter of FIG. 2, taken along line 3B-3B of FIG.2.

FIG. 4 is a side illustration of an embodiment of a stiffening shaft andhub of the catheter of FIG. 1.

FIG. 5 is a side illustration of another embodiment of a catheter forcalculating a Fractional Flow Reserve (FFR) with the proximal shaft inthe radially expanded configuration.

FIG. 6 is a side illustration of the catheter of FIG. 5 with theproximal shaft in the radially collapsed configuration.

FIG. 7A is a cross-sectional illustration of an embodiment of theproximal shaft of the catheter of FIG. 5, taken along line 7A-7A of FIG.5.

FIG. 7B is a cross-sectional illustration of an embodiment of theproximal shaft of the catheter of FIG. 6, taken along line 7B-7B of FIG.6.

FIG. 8 is a side illustration of an embodiment of the stiffening shaftand hub of the catheter of FIG. 5.

FIG. 9 is a side illustration of another embodiment of a catheter forcalculating a Fractional Flow Reserve (FFR) in a first configuration.

FIG. 9A is a detail view of portion A of FIG. 9.

FIG. 10 is a side illustration of the catheter of FIG. 9 in a secondconfiguration.

FIG. 10A is detailed view of section B of FIG. 10 as the movable shaftis being removed.

FIG. 10B is a detailed view of section B of FIG. 10 with the movableshaft removed.

FIG. 11A is a cross-sectional illustration of an embodiment of aproximal shaft of the catheter of FIG. 9, taken along line 11A-11A ofFIG. 9.

FIG. 11B is a cross-sectional illustration of an embodiment of theproximal shaft of the catheter of FIG. 10, taken along line 11B-11B ofFIG. 10.

FIG. 12 is a side illustration of another embodiment of a catheter forcalculating a Fractional Flow Reserve (FFR) with a distal portion of theproximal shaft in a radially expanded configuration.

FIG. 13 is a side illustration of the catheter of FIG. 12 with thedistal portion of the proximal shaft in a radially collapsedconfiguration.

FIG. 14A is a cross-sectional illustration of an embodiment of thedistal portion of the proximal shaft of the catheter of FIG. 12, takenalong line 134-14A of FIG. 12.

FIG. 14B is a cross-sectional illustration of an embodiment of thedistal portion of the proximal shaft of the catheter of FIG. 13, takenalong line 14B-14B of FIG. 13.

FIG. 15 is a side illustration of another embodiment of a catheter forcalculating a Fractional Flow Reserve (FFR) with a distal portion of aproximal shaft in a radially expanded configuration.

FIG. 16 is a side illustration of the catheter of FIG. 15 with thedistal portion of the proximal shaft in a radially collapsedconfiguration.

FIG. 17A is a cross-sectional illustration of an embodiment of thedistal portion of the proximal shaft of the catheter of FIG. 15, takenalong line 17A-17A of FIG. 15

FIG. 17B is a cross-sectional illustration of an embodiment of thedistal portion of the proximal shaft of the catheter of FIG. 16, takenalong line 17B-17B of FIG. 16.

FIG. 18 is a side illustration of another embodiment of a catheter forcalculating a Fractional Flow Reserve (FFR) with an expandable portionof a distal in a radially expanded configuration.

FIG. 19 is a side illustration of the catheter of FIG. 18 with theexpandable portion a radially collapsed configuration.

FIG. 20A is a cross-sectional illustration of an embodiment of theexpandable portion of the catheter of FIG. 18, taken along line 20A-20Aof FIG. 18

FIG. 20B is a cross-sectional illustration of an embodiment of theexpandable portion of the catheter of FIG. 19, taken along line 20B-20Bof FIG. 19.

DETAILED DESCRIPTION OF THE INVENTION

Specific embodiments of the present invention are now described withreference to the figures, wherein like reference numbers indicateidentical or functionally similar elements. The terms “distal” and“proximal”, when used in the following description to refer to acatheter or delivery system are with respect to a position or directionrelative to the treating clinician. Thus, “distal” and “distally” referto positions distant from, or in a direction away from the treatingclinician, and the terms “proximal” and “proximally” refer to positionsnear, or in a direction toward the clinician. The terms “distal” and“proximal”, when used in the following description to refer to a vesselor a stenosis are used with reference to the direction of blood flow.Thus, “distal” and “distally” refer to positions in a downstreamdirection with respect to the direction of blood flow, and the terms“proximal” and “proximally” refer to positions in an upstream directionwith respect to the direction of blood flow.

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Although the description of the invention is in the contextof treatment of blood vessels such as the coronary arteries, theinvention may also be used in any other body passageways where it isdeemed useful such as but not limited to peripheral arteries, carotidarteries, renal arteries, and/or venous applications. Furthermore, thereis no intention to be bound by any expressed or implied theory presentedin the preceding technical field, background, brief summary or thefollowing detailed description.

Referring to FIGS. 1-4, a catheter (or micro-catheter) 100 forcalculating a Fractional Flow Reserve (FFR) according to an embodimentof the present disclosure is shown. The catheter 100 includes a proximalshaft 102, a distal shaft 108, a pressure sensor 118, and at least onepressure sensor wire 120. The catheter 100 may further include a hub orhandle 126 coupled to a proximal end of the proximal shaft 102 forconvenient handling of the catheter 100, as shown in FIGS. 1 and 2. Thecatheter 100 is configured to be disposed in a vessel 900 with aproximal portion of the proximal shaft 102 extending outside of apatient, and a distal portion of the distal shaft 108 positioned in situwithin a lumen 910 of the vessel 900 having a lesion or stenosis 902.The catheter 100 is configured to measure a distal pressure P_(d) on adistal side 906 of the stenosis 902. Various features of the componentsof the catheter 100 reflected in FIGS. 1-4 and described below can bemodified or replaced with different structures and/or mechanisms.

In an embodiment, the proximal shaft 102 of the catheter 100 includes aproximal end 104 and a distal end 106. The proximal shaft 102 includesan expansion lumen 128 extending therethrough from the proximal end 104to the distal end 106, as shown in FIG. 1. However, it is not necessaryfor the expansion lumen 128 to extend to the distal end 106 of theproximal shaft. In other embodiments, the expansion lumen 128 may stopproximally of the distal end 106, but preferably at least to a locationwhere the proximal shaft 102 exits the guide catheter 920 (describedbelow). The proximal shaft 102 includes a radially expandedconfiguration (FIGS. 1 and 3A) and a radially collapsed configuration(FIGS. 2 and 3B). The expansion lumen 128 of the proximal shaft 102 isconfigured to receive a stiffening shaft 130 such that with thestiffening shaft 130 received with the expansion lumen 128, the proximalshaft 102 is in the radially expanded configuration and with thestiffening shaft 130 not received within the expansion lumen 128, theproximal shaft 102 is in the radially collapsed configuration. Thus, theproximal shaft 102 has a first outer diameter D1 when in the radiallyexpanded configuration and a second outer diameter D2 when in theradially collapsed configuration, with the first outer diameter D1 beinggreater than the second outer diameter D2, as shown in FIGS. 3A-3B. Asused herein, the term “diameter” does not have to refer to a circularprofile, but instead is used generally to refer to a cross-sectionaldimension.

The proximal shaft 102 may be formed of a shape-memory material with apre-set shape. In the embodiment of FIGS. 1-3B, the proximal shaft 102has a pre-set shape in the radially collapsed configuration, as shown inFIGS. 2 and 3B. Due to the shape memory material and pre-set shapethereof, the proximal shaft 102 actively recoils to the radiallycollapsed configuration upon removal of the stiffening shaft 130 fromthe expansion lumen 128. The proximal shaft 102 may be formed of, forexample, and not by way of limitation, polyether block amide (e.g.,VESTAMID or PEBAX), thermoplastic elastomers (TPE), or other materialssuitable for the purposes described herein. The proximal shaft 102 maybe coupled to the hub/handle 126 by, for example, and not by way oflimitation, adhesives, mechanical connection, fusing, welding, for anyother method suitable for the purposes of the present disclosure.

FIGS. 1-2 show an embodiment of the distal shaft 108 of the catheter100. The distal shaft 108 includes a proximal end 110 and a distal end112. A guidewire lumen 114 extends from the proximal end 110 to thedistal end 112. The distal shaft 108 further includes the pressuresensor 118 and a distal portion of the pressure sensor wire 120. Thedistal shaft 108 is configured to extend from a proximal side 904 of thestenosis 902 to the distal side 906 of stenosis 902 such that thepressure sensor 118 is disposed on the distal side 906 of stenosis 902,as shown in FIGS. 1-2. The guidewire lumen 114 is configured to receivea guidewire 116 therein. A proximal guidewire port 168 is disposed atthe proximal end 110 of the distal shaft 108. A distal guidewire port113 is disposed at the distal end 112 of the distal shaft 108. Thedistal portion of the pressure sensor wire 120 is disposed within adistal shaft wall 122 of the distal shaft 108. The distal shaft 108 maybe formed of, for example, and not by way of limitation, polyethylene,polyether block amide (e.g., VESTAMID or PEBAX), polyamide and/orcombinations thereof, either blended or co-extruded, or other materialssuitable for the purposes described herein. The distal shaft 108 may becoupled to the proximal shaft 102 by, for example, and not by way oflimitation, adhesives, fusing, welding, for any other method suitablefor the purposes of the present disclosure. In other embodiments, theproximal shaft 102 and the distal shaft 108 may be formed unitarily.

The pressure sensor 118 of the distal shaft 108, as shown in FIGS. 1-2,may be a piezo-resistive pressure sensor, a piezo-electric pressuresensor, a capacitive pressure sensor, an electromagnetic pressuresensor, an optical pressure sensor, and/or combinations thereof or othersensors suitable for the purpose described herein. The pressure sensor118 is configured to measure a pressure of a fluid outside the distalshaft 108. With the pressure sensor 118 disposed on the distal side 906of the lesion 902, the pressure sensor 118 measures the distal pressureP_(d) of a fluid outside of the distal shaft 108. The pressure sensor118 is further configured to communicate the distal pressure P_(d) witha processor 140. The pressure sensor 118 is coupled to the distal shaft108 of the catheter 100 such that the pressure sensor 118 is disposed onthe distal side 906 of stenosis 902 when the distal shaft 108 ispositioned at a treatment site therein, as shown in FIGS. 1-2. Thepressure sensor 118 is coupled to the distal shaft 108 by, for exampleand not by way of limitation, adhesives, fusing, welding, for any othermethod suitable for the purposes of the present disclosure. Further,additional features may be provided as part of the distal shaft 108 forhousing the pressure sensor 118, such as pockets, openings, and similarfeatures.

The pressure sensor wire(s) 120 include(s) a proximal end coupled to theprocessor 140 and a distal end 121 coupled to the pressure sensor 118.The pressure sensor wire(s) 120 is/are configured such that pressuresensor 118 is in communication with the processor 140. The pressuresensor wire(s) 120 may be disposed within the proximal shaft wall 124 ofthe proximal shaft 102 and a corresponding distal shaft wall 122 of thedistal shaft 108 such that the pressure sensor wire(s) 120 extend(s)proximally from the pressure sensor 118, through the distal shaft wall122, through the corresponding proximal shaft wall 124, exiting throughthe hub/handle 126 to the processor 140. The pressure sensor wire(s) 120may be coupled to the pressure sensor 118 by, for example, and not byway of limitation, adhesives, fusing, welding, or any other methodsuitable for the purposes of the present disclosure. The pressure sensorwire(s) 120 may be coupled to the processor 140 by, for example and notby way of limitation, cables, connectors, antennas, routers, switches,or any other coupling suitable for the purposes described herein.

While FIGS. 3A-3B show three (3) pressure sensor wires 120, this is notmeant to limit the design, and more or fewer pressure sensor wires 120may be utilized. Moreover, the pressure sensor wires 120 may beeliminated in embodiments wherein a signal from the pressure sensor 118is sent to the processor 140 other than via the pressure sensor wires120, such as, but not limited to, a wireless transmission.

The processor 140 may be any processor suitable for the purposesdescribed herein. The processor 140 may include such components as aCPU, a display device, an amplification and filtering device, ananalog-to-digital converter, and various other components. The processor140 is configured to receive a measured proximal pressure P_(a) and ameasured distal pressure P_(d). The processor 140 is further configuredto provide a continuous display of calculated Fractional Flow Reserve(FFR). The processor 140 is coupled to the pressure sensor wires(s) 120such that the processor 140 is in communication with the pressure sensor118 as described previously. The processor 140 may be coupled to aproximal end of the pressure sensor wire(s) 120 via variouscommunication pathways, including but not limited to one or morephysical connections including electrical, optical, and/or fluidconnections, a wireless connection, and/or combinations thereof.Accordingly, it is understood that additional components (e.g., cables,connectors, antennas, routers, switches, etc.) not illustrated in FIGS.1-4 may include devices to facilitate communication between the proximalend of the pressure sensor wire(s) 120 and the processor 140. In otherembodiments, instead of the pressure sensor wire(s) 120, communicationbetween the pressure sensor 118 and the processor 140 may beaccomplished wirelessly.

The stiffening shaft 130 may be a solid core wire. The stiffening shaft130 is configured to be movable within the expansion lumen 128 of theproximal shaft 102, as shown in FIGS. 1-2. The stiffening shaft 130 isfurther configured such that when disposed within the expansion lumen128 of the proximal shelf 102, the stiffening shaft 130 expands theproximal shaft 102 to the radially expanded configuration (FIGS. 1 and3A). The stiffening shaft 130, when so disposed, is configured toprovide strength and pushability to the proximal shaft 102 for deliveryof the catheter 100 to the desired treatment site. The stiffening shaft130 is further configured such that upon removal from the expansionlumen 128 of the proximal shaft 102, the proximal shaft 102 collapses tothe radially collapsed configuration (FIGS. 2 and 3B). An outer surfaceof the stiffening shaft 130 may have a lubricious coating thereon. Thestiffening shaft 130 may be formed of, for example, and not by way oflimitation, metals such as stainless steel, cobalt, chromium, nickeland/or molybdenum based alloys (MP35N, MP20N, L605), nickel titaniumalloys (NITINOL) or combinations thereof. The stiffening shaft 130 maybe made of other materials provided that the stiffening shaft providessufficient strength and pushability for the purposes described herein.The lubricious coating on the outer surface of the stiffening shaft 130may be polytetrafluoroethylene (PTFE) or any other materials suitablefor purposes of the present disclosure.

In an embodiment shown in FIG. 4, the hub 126 of the catheter 100includes a proximal end 136 and a distal end 138. The hub 126 defines astiffening shaft lumen 139 therein between the proximal end 136 and thedistal end 138. The stiffening shaft lumen 139 is disposed within thehub 126 such that the stiffening shaft lumen 139 aligns longitudinallywith the expansion lumen 128, effectively creating a continuous lumenfrom proximal end 136 of the hub 126 extending distally through theproximal end 104 of the proximal shaft 102 to the distal end 106 of theproximal shaft 102 (FIG. 1) and configured to receive the stiffeningshaft 130 therein. The stiffening shaft 130 is configured to be movablewithin both the stiffening shaft lumen 139 of hub 126 and the expansionlumen 128 of the proximal shaft 102.

With an understanding of the components of catheter 100, it is nowpossible to describe the interactions of the various components and amethod to calculate a Fractional Flow Reserve (FFR). Referring back toFIGS. 1-2, a guide catheter 920 and the guidewire 116 are advancedthrough the vasculature to a desired site. The guidewire 116 may beback-loaded into the catheter 100 (i.e., the proximal end of theguidewire 116 is loaded into the distal end of the guidewire lumen 114at the distal end 112 of distal shaft 108). The catheter 100, with theproximal shaft 102 in the radially expanded configuration (i.e., withthe stiffening shaft 130 disposed within the expansion lumen 128) maythen be advanced over the guidewire 116 and through a lumen 928 of theguide catheter 920 to the desired treatment site. In particular, with adistal end (not shown) of the guide catheter 920 disposed at a desiredsite proximal of the stenosis 902, such as in the sinus of an aorticvalve, the distal shaft 108 of the catheter 100 is advanced through thelumen 928 and distal of the distal end of the guide catheter 920. Thecatheter 100 is advanced such that distal shaft 108 is disposed acrossthe stenosis 902 of the vessel 900.

With the catheter 100 in position at the treatment site, the stiffeningshaft 130 is removed from the expansion lumen 128 of the proximal shaft102. Removing the stiffening shaft 130 results in the proximal shaft 102collapsing to the radially collapsed configuration with second outerdiameter D2, as shown in FIGS. 2 and 3B. With the proximal shaft 102 inthe radially collapsed configuration, the combination of the guidewire116 and the proximal shaft 102 occupies a smaller percentage of thelumen 928 of the guide catheter 920, as shown by comparing FIG. 3B toFIG. 3A. With the catheter 100 in position and the proximal shaft 102 inthe radially collapsed configuration, the appropriate pressuremeasurements may be taken. Thus, blood flow adjacent the distal end ofthe guide catheter 920 fills the lumen 928 and tubing 924 via a port 926in a proximal portion of the guide catheter 920. The proximal pressureP_(a) at the distal end of the guide catheter 920 is measured by anexternal pressure transducer 922 via the fluid (blood) column extendingthrough the lumen 928 and the tubing 922. Thus, the external pressuretransducer 922 is configured to measure proximal or aortic (AO) pressureP_(a) at the distal end of the guide catheter 920.

The external pressure transducer 922 is configured to communicate themeasured proximal pressure P_(a) to the processor 140 via a pressuretransducer wire 929, as shown in FIG. 2. However, this is not meant tolimit the design and the external pressure transducer 922 maycommunicate with the processor 140 by any means suitable for thepurposes described, including, but not limited to, electrical cables,optical cables, or wireless devices. Simultaneously, the pressure sensor118 measures distal pressure P_(d) distal of the stenosis 902. Thedistal pressure P_(d) is communicated to the processor 140, as explainedabove. The processor 140 calculates the Fractional Flow Reserve (FFR)based on the distal pressure P_(d) divided by the proximal/aorticpressure P_(a), or FFR=P_(d)/P_(a).

As explained above, the catheter 100 with the proximal shaft 102 in theradially collapsed configuration has a reduced cross-sectional profile(FIG. 3B) as compared to the proximal shaft 102 in the radially expandedconfiguration (FIG. 3A). As further explained above, because theproximal or aortic pressure P_(a) is measured using the fluid columnwithin the lumen 928 of the guide catheter 920 between an outer surfaceof a guidewire/proximal shaft combination and an inner surface of theguide catheter, a larger profile may lead to errors in the measuredproximal or aortic pressure P_(a). Such errors are carried through tothe FFR calculation noted above because the measured proximal pressureP_(a) is used in the FFR calculation. Thus, reducing the cross-sectionalprofile leads to a smaller potential for error in the proximal pressureP_(a), and hence a smaller potential for error in the FFR calculation.Since the size of the guidewire 116 remains constant, the smaller thecross-sectional profile of the proximal shaft 102, the smaller thepotential error in proximal (AO) pressure measurement P_(a). Statedanother way, the smaller the cross-sectional profile of the proximalshaft 102 of the catheter 100, the more accurate the proximal (AO)pressure measurement P_(a), and therefore a more accurate FFR value.

Referring to FIGS. 5-8B, a catheter (or micro-catheter) 200 forcalculating a Fractional Flow Reserve (FFR) according to anotherembodiment of the present disclosure is shown. The catheter 200 includesa proximal shaft 202, a distal shaft 208, a pressure sensor 218, and atleast one pressure sensor wire 220, as shown in FIGS. 5-7B and describedin greater detail below. The distal shaft 208, the pressure sensor 218,and the at least one pressure sensor wire 220 are similar to the distalshaft 108, the pressure sensor 118, and the at least one pressure sensorwire 120 of the catheter 100 of FIGS. 1-4. Therefore, details of thedistal shaft 208, the pressure sensor 218, and the at least one pressuresensor wire 220 will not be repeated here. The catheter 200 isconfigured to be disposed with a proximal portion of the proximal shaft202 extending outside of a patient, and a distal portion of the distalshaft 208 positioned in situ within a lumen 910 of a vessel 900 having astenosis or lesion 902. The catheter 200 is configured such that thecatheter 200 measures a distal pressure P_(d) of blood on a distal side906 of the stenosis 902.

In an embodiment, the proximal shaft 202 of the catheter 200 includes aproximal end 204, a distal end 206, and an expansion lumen 228 extendingfrom the proximal end 204 to the distal end 206 of the proximal shaft202. However, it is not necessary for the expansion lumen 228 to extendto the distal end 206 of the proximal shaft 202. In other embodiments,the expansion lumen 228 may stop proximally of the distal end 206, butpreferably extends distally at least to a location where the proximalshaft 202 exits the guide catheter. The proximal shaft 202 includes aradially expanded configuration (FIGS. 5 and 7A) and a radiallycollapsed configuration (FIGS. 6 and 7B). The expansion lumen 228 of theproximal shaft 202 is configured to receive a stiffening shaft 230 suchthat with the stiffening shaft 230 received within expansion lumen 228,the proximal shaft 202 is in the radially expanded configuration, andwith the stiffening shaft 230 not received with expansion lumen 228, theproximal shaft 202 is in the radially collapsed configuration. Theproximal shaft 202 has a first outer diameter D3 when in the radiallyexpanded configuration and a second outer diameter D4 when in theradially collapsed configuration, with the first outer diameter D3 beinggreater than the second outer diameter D4, as shown in FIGS. 7A-7B. Theproximal shaft 202 is disposed distal of and coupled to a hub 226 forconvenient handling of the catheter 200. The proximal shaft 202 may becoupled to the hub 226 by, for example and not by way of limitation,adhesives, fusing, welding, for any other method suitable for thepurposes of the present disclosure.

The proximal shaft 202 may be formed of a shape-memory configurationwith a pre-set shape, non-limiting examples of which are described inU.S. Pat. No. 9,192,751 to Macaulay et al., which is incorporated byreference herein in its entirety. In the embodiment of FIGS. 5-7B, theproximal shaft 202 has a pre-set shape in the radially collapsedconfiguration with the second outer diameter D4. Due to the shape memorymaterial and pre-set shape thereof, the proximal shaft 202 of thecatheter 200 actively recoils to the radially collapsed configurationafter removal of the stiffening shaft 230 from the expansion lumen 228.

FIGS. 7A-7B illustrate an embodiment of how the proximal shaft 202 isconfigured to collapse upon removal of the stiffening shaft 230 from theexpansion lumen 228. In such an embodiment, the proximal shaft 202includes an elastic frame 254, a liner 250, and a jacket 252. Theelastic frame 254 may be coupled between the liner 250 and the jacket252 by lamination, embedding, or other methods suitable for the purposesdescribed herein. Although not shown in the drawings, elastic frame 254is generally tubular. The elastic frame 254 may assume various shapessuitable for the purposes described herein, embodiments of which aredescribed in detail in U.S. Pat. No. 9,192,751 to Macaulay et al., whichis incorporated herein by reference in its entirety. Therefore, thedetails of elastic frame 254 will not be repeated here. The elasticframe 254 may be formed of materials such as, but not limited to,nickel-titanium alloys (e.g. NITINOL), nickel-cobalt-chromium-molybdenumalloys (e.g. MP35N), stainless steel, high spring temper steel, or anyother metal or elastomer or composite having elastic properties topermit expansion and recoil suitable for purposes of the presentdisclosure. The liner 250 may be constructed of materials such as, butnot limited to, polytetrafluoroethylene (PTFE; e.g. Teflon®),polyethylene, polyethylene terephthaiate (PET), polyester, or othermaterials suitable for the purposes of the present disclosure. Thejacket 252 may be constructed of materials such as, but not limited to,polyurethane (e.g. Peliethane©, Eiasthane™, Texin®, Tecothane®),polyamide polyether block copolymer (e.g. Pebax®, nylon 12),polyethylene, TPE, Propel, Fuoroguard or other materials suitable forthe purposes of the present disclosure.

The elastic frame 254 is of a shape memory material with a pre-setshape. In an embodiment, the elastic frame 254 has a pre-set shape inthe radially collapsed configuration as shown in FIG. 7B. The elasticframe 254 enables the proximal shaft 202 to expand to the radiallyexpanded configuration with the first outer diameter D3, as shown inFIG. 7A. Due to the shape memory material and pre-set shape thereof, theelastic frame 254 causes the proximal shaft 202 to actively recoil tothe radially collapsed configuration after removal of the stiffeningshaft 230 from the expansion lumen 228 of the proximal shaft 202.

The liner 250 is circumferentially continuous and forms the expansionlumen 228, as shown in FIG. 7A. The elastic frame 254 and the jacket 252are non-circumferentially continuous. Accordingly, a circumferentialjacket gap 258 is disposed between a first circumferential end 270 and asecond circumferential end 272 of jacket 252, as shown in FIG. 7A. Inthe radially collapsed configuration, as shown in FIG. 7B, the liner 250folds to form a liner overlap portion 262 defined by at least one fold.In one embodiment, overlap portion 262 is defined by an inner fold 264and an outer fold 266 of the liner 250. When the liner 250 folds by theradial collapse of the elastic frame 254, the liner 250 forms the lineroverlap portion 262, and the first circumferential end 270 and thesecond circumferential 272 of the jacket 252 move closer together, asshown in FIG. 7B. Thus, the circumferential jacket gap 258 is reduced insize, as shown by comparing FIGS. 7A and 7B. In the radially expandedconfiguration, the inner fold 264 and the outer fold 266 are flattenedor stretched apart such that the first and second circumferential ends270, 272 of the jacket 252 move apart from each other, therebyincreasing the circumferential jacket gap 258, as shown in FIG. 7A.

The stiffening shaft 230 may be a solid core wire, as explained abovewith respect to the stiffening shaft 130. The stiffening shaft 230 isconfigured to be movable within the expansion lumen 228 of the proximalshaft 202 as shown in FIGS. 5-6. The stiffening shaft 230 is furtherconfigured such that when disposed within the expansion lumen 228 of theproximal shaft 202, the stiffening shaft 230 expands the proximal shaft202 to the radially expanded configuration (FIGS. 5 and 7A). Thestiffening shaft 230, when so disposed, is configured to providestrength and pushability to the proximal shaft 202 for delivery of thecatheter 200 to the desired treatment site. The stiffening shaft 230 isfurther configured such that upon removal of the stiffening shaft 230from the expansion lumen 228 of the proximal shaft 202, the proximalshaft 202 collapses to the radially collapsed configuration (FIGS. 6 and7B). An outer surface of the stiffening shaft 230 may have a lubriciouscoating thereon. The stiffening shaft 230 may be formed of, for example,and not by way of limitation, metals such as stainless steel, cobalt,chromium, nickel and/or molybdenum based alloys (MP35N, MP20N, L605),nickel titanium alloys (NITINOL) or combinations thereof. The stiffeningshaft 230 may be made of other materials provided that the stiffeningshaft provides sufficient strength and pushability for the purposesdescribed herein. The lubricious coating on the outer surface of thestiffening shaft 230 may be polytetrafluoroethylene (PTFE) or any othermaterials suitable for purposes of the present disclosure.

In an embodiment shown in FIG. 8, the hub 226 of the catheter 200includes a proximal end 236 and a distal end 238. A short stiff shaft232 is coupled to the distal end 238 of the hub 226. The short stiffshaft 232 extends distally within a proximal portion 205 of theexpansion lumen 228 of the proximal shaft 202. The short stiff shaft 232provides strength and pushability to the proximal portion 205 of theproximal shaft 202. A stiffening shaft exit port 234 is in communicationwith the expansion lumen 228 for entry and exit of the stiffening shaft230 to the expansion lumen 228. The stiffening shaft 230 is configuredto be movable within expansion shaft 228 via the stiffening shaft exitport 234. The design of the proximal shaft 202 with the stiffening shaftexit port 234 and the short stiff shaft 232 may be interchanged withother embodiments herein. For example, and not by way of limitation, theproximal shaft 102 of the embodiment of FIGS. 1-4 may be used with thestiffening shaft exit port 234 and the short stiff shaft 232 of theembodiment of FIGS. 5-8. Similarly, the proximal shaft 202 of theembodiment of FIGS. 5-8 may be used with the manner in which thestiffening shaft 130 is introduced and removed from the proximal shaft102 of FIGS. 1-4.

With an understanding of the components of catheter 200, theinteractions of the various components and a method to calculate aFractional Flow Reserve (FFR) will now be described. Referring back toFIGS. 5-6, a guide catheter (not shown but may be similar to guidecatheter 920 of FIGS. 1-2) and the guidewire 216 are advanced throughthe vasculature to a desired site. The guidewire 216 may be back-loadedinto the catheter 200 (i.e., the proximal end of the guidewire 216 isloaded into the distal end of the guidewire lumen 214 at the distal end212 of the distal shaft 208). The catheter 200, with the proximal shaft202 in the radially expanded configuration (i.e., with the stiffeningshaft 230 disposed within the expansion lumen 228) may then be advancedover the guidewire 216 and through a lumen of the guide catheter to thedesired treatment site. In particular, with a distal end (not shown) ofthe guide catheter disposed at a desired site proximal of the stenosis902, such as in the sinus of an aortic valve, the distal shaft 208 ofthe catheter 200 is advanced through the lumen of the guide catheter anddistal of the distal end of the guide catheter. The catheter 200 isadvanced such that distal shaft 208 is disposed through the stenosis 902of the vessel 900.

With the catheter 200 in position at the treatment site, the stiffeningshaft 230 is removed from the expansion lumen 228 of the proximal shaft202. Removing the stiffening shaft 230 results in the proximal shaft 202collapsing to the radially collapsed configuration with the second outerdiameter D3, as shown in FIGS. 6 and 7B. With the proximal shaft 202 inthe radially collapsed configuration, the combination of the guidewire216 and the proximal shaft 202 occupies a smaller percentage of thelumen of the guide catheter, as shown by comparing FIG. 7B to FIG. 7A.With the catheter 200 in position and the proximal shaft 202 in theradially collapsed configuration, the appropriate pressure measurementsmay be taken. Thus, blood flow adjacent the distal end of the guidecatheter fills the lumen of the guide catheter and tubing via a port ina proximal portion of the guide catheter. The proximal pressure P_(a) atthe distal end of the guide catheter is measured by an external pressuretransducer via the fluid (blood) column extending through the lumen ofthe guide catheter and the tubing. Thus, the external pressuretransducer is configured to measure the proximal or aortic (AO) pressureP_(a) at the distal end of the guide catheter.

The external pressure transducer is configured to communicate themeasured proximal pressure P_(a) to a processor 240 via a pressuretransducer wire, similar to as described above with respect to FIG. 2.Simultaneously, the pressure sensor 218 measures the distal pressureP_(d) distal of the stenosis 902. The distal pressure P_(d) iscommunicated to the processor 240, as explained above. The processor 240calculates the Fractional Flow Reserve (FFR) based on the distalpressure P_(d) divided by the proximal/aortic pressure P_(a), orFFR=P_(d)/P_(a).

As explained above, the catheter 200 with the proximal shaft 202 in theradially collapsed configuration has a reduced cross-sectional profile(FIG. 7B) as compared to the proximal shaft 202 in the radially expandedconfiguration (FIG. 7A). As further explained above, because theproximal or aortic pressure P_(a) is measured using the fluid columnwithin the lumen of the guide catheter between an outer surface of aguidewire/proximal shaft combination and an inner surface of the guidecatheter, a larger profile may lead to errors in the measured proximalor aortic pressure P_(a). Such errors are carried through to the FFRcalculation noted above because the measured proximal pressure P_(a) isused in the FFR calculation. Thus, reducing the cross-sectional profileleads to a smaller potential for error in the proximal pressure P_(a),and hence a smaller potential for error in the FFR calculation. Sincethe size of the guidewire 216 remains constant, the smaller thecross-sectional profile of the proximal shaft 202, the smaller thepotential error in measured proximal (AO) pressure P_(a). Stated anotherway, the smaller the cross-sectional profile of the proximal shaft 202of the catheter 200, the more accurate the measured proximal (AO)pressure P_(a), and therefore a more accurate FFR value is calculated.

Referring to FIGS. 9-11B, a catheter (or micro-catheter) 500 forcalculating a Fractional Flow Reserve (FFR) according to anotherembodiment of the present disclosure is shown. The catheter 500 includesa proximal shaft 502, a distal shaft 508, transition shaft 570, apressure sensor 518, at least one pressure sensor wire 520, and amovable shaft 542. The distal shaft 508, the pressure sensor 518, andthe at least one pressure sensor wire 520 are similar to the distalshaft 108, the pressure sensor 118, and the at least one pressure sensorwire 120 of the catheter 100 of FIGS. 1-4. Therefore, details of thedistal shaft 508, the pressure sensor 518, and the at least one pressuresensor wire 520 will not be repeated here. The catheter 500 isconfigured to be disposed with a proximal portion of the proximal shaft502 extending outside of a patient, and a distal portion of the distalshaft 508 positioned in situ within a lumen 910 of a vessel 900 having astenosis or lesion 902. The catheter 500 is configured such that thecatheter 500 measures a distal pressure P_(d) of blood in the vessel 900on a distal side 906 of the stenosis 902.

The catheter 500 includes a first configuration (FIGS. 9, 9A and 11A)with the movable shaft 542 disposed over the proximal shaft 502, and asecond configuration (FIGS. 10, 10B and 11B) with the movable shaft 542not disposed over the proximal shaft 502. The first configuration isgenerally used to deliver the catheter 500 through the vasculature tothe desired treatment site. Thus, with the movable shaft 542 disposedover the proximal shaft 502, the movable shaft 542 provides strength andpushability to the proximal shaft 502. When at the desired treatmentsite, the movable shaft 542 may be retracted proximally such that theproximal shaft 502 occupies a smaller area of the guide catheter.

As noted above, the catheter 500 includes a transition shaft 570. Thetransition shaft 570 is disposed between the proximal shaft 502 and thedistal shaft 508. Thus, a proximal end 572 of the transition shaft 570is disposed adjacent a distal end 506 of the proximal shaft 502 and adistal end 574 of the transition shaft 570 is disposed adjacent aproximal end 510 of the distal shaft 508. The transition shaft 570serves as a transition from the proximal shaft 502 to the distal shaft508. The transition shaft 570 includes a guidewire port 576 for entry ofthe guidewire 516 into the transition shaft 570 and the distal shaft508. Although the transition shaft 570 is described separately in theembodiment of FIGS. 9-11B, the transition shaft may be considered partof the distal shaft 508. Further, other embodiments described herein mayinclude such a transition shaft even if not specifically described, andthe present embodiment need not include a transition shaft.

In an embodiment, the proximal shaft 502 may be a hollow shaft with thepressure sensor wire(s) 520 disposed within a central passageway of thehollow shaft. The proximal shaft 502 includes a proximal end 504 coupledto a hub/handle 526 and a distal end 506 coupled to the transition shaft570. The proximal shaft 502 is disposed distal of and coupled to ahub/handle 526. It is desirable for the proximal shaft to have aminimized cross-sectional profile in order to occupy a smallerpercentage of a passageway of a guide catheter. In an embodiment, theproximal shaft 502 has an outer diameter of approximately 0.014 inch,which is equivalent to the outer diameter of FFR wires. The proximalshaft 502 may be formed of materials such as, but not limited to,stainless steel, cobalt, chromium, nickel and/or molybdenum based alloys(MP35N, MP20N, L605), nickel titanium alloys (NITINOL) or combinationsthereof. The proximal shaft 502 may also be formed of materials such,but not limited to, polyethylene, polyether block amide (PEBA, e.g.VESTAMID, PEBAX), thermoplastic elastomers (TPE), polyamide and/orcombinations thereof, either blended or co-extruded, or other materialssuitable for the purposes described herein. The proximal shaft 502 maybe coupled to the hub 526 by, for example, and not by way of limitation,adhesives, fusing, welding, for any other method suitable for thepurposes of the present disclosure.

In an embodiment, the movable shaft 542 is generally tubular with ac-shape cross-section, as shown in FIGS. 9 and 11A. The movable shaft542 includes a proximal end 546 and a distal end 548. The movable shaft542 includes a lumen 544 extending from the proximal end 546 to thedistal end 548 (FIG. 11A). The movable shaft 542 further includes agroove 550 extending longitudinally from the proximal end 546 distallyto the distal end 548. Groove 550 also extends radially from an innersurface of the movable shaft 542 to an outer surface of the movableshaft 542, as shown in FIG. 11A. The movable shaft 542 is configured tobe slidably disposed over the proximal shaft 502 such that when themovable shaft 542 is disposed over the proximal shaft 502, the catheter500 is in the first configuration (FIGS. 9 and 11A), and when themovable shaft 542 is not disposed over the proximal shaft, the catheter500 is in the second configuration (FIGS. 10 and 11B). The movable shaft542 is further configured to be selectively coupled to the hub 526 suchthat with the movable shaft 542 disposed over the proximal shaft 502 andselectively coupled to the hub 526, the distal end 548 of the movableshaft 542 contacts a proximal end 572 of the transition shaft 570 (FIGS.9, 9A) (the first configuration). In this first configuration, adistally directed force DF applied to the hub 526 is transferred to themovable shaft 542 coupled thereto. The distally directed force DF istransferred along the movable shaft 542. The distal end 548 of themovable shaft 542 transfers the distally directed force DF to theproximal end 572 of the transition shaft 570 (FIGS. 9 and 9A). Thus,with the movable shaft 542 in the first configuration, the movable shaft542 provides strength and pushability to the catheter 500 for deliveryto the desired treatment site.

The groove 550 in the movable shaft 542 is a longitudinal grooveconfigured such that the movable shaft 542 may be advanced or retractedover the proximal shaft 502 while providing an exit for the proximalportion of the pressure sensor wire(s) 520. Thus, the groove 550 issized such that pressure sensor wire(s) 520 may exit through the groove550. While the groove 550 is desirable, it is not necessary. If themovable shaft 542 did not include a groove 550, when the movable shaft542 is retracted, the portion of the pressure sensor wire(s) 520proximal of the hub 526 would need to be at least as long as the movableshaft 542 in order to provide room for the movable shaft 542 to retractover the pressure sensor wire(s) 520 proximal of the hub 526. Byproviding the groove 550, the proximal portion of the pressure sensorwires(s) 520 may exit the movable shaft 542 through the groove 550 atany longitudinal position of the movable shaft 542. The moveable shaft542 may be formed of, for example, and not by way of limitation,polyethylene, polyether block amide (PEBA, e.g. VESTAMID, PEBAX),thermoplastic elastomers (TPE), polyimide and/or combinations thereof,either blended or co-extruded, or other materials suitable for thepurposes described herein. The movable shaft 542 may be selectivelycoupled to the hub 526 by a mechanical locking mechanism disposed withthe hub 526 and actuated by a trigger, coupling mechanisms suitable forthe purposes described herein. For example, and not by way oflimitation, the movable shaft 542 may be selectively coupled to the hub526 by a locking key/pin arrangement, a reversible snap fit connection,an interference fit, or other suitable couple mechanisms.

By utilizing the movable shaft 542 disposed over the proximal shaft 502,the proximal shaft 502 can have a smaller cross-sectional profile thanwould be required for pushability without the movable shaft 542. Thus,with the movable shaft 542 in the first configuration (FIGS. 9 and 11A),the proximal portion of the catheter 500 has a first outer diameter D5(FIG. 11A) which is the outer diameter of the movable shaft 542. Thecombined strength of the proximal shaft 502 and the movable shaft 542provides sufficient strength and pushability for the delivering thecatheter 500 to the desired treatment site. Once at the desiredtreatment site, the movable shaft 542 may be retracted proximally andwithdrawn (FIGS. 10, 10A, 10B, and 11B) such that the proximal portionof the catheter 500 has a second outer diameter D6 which is smaller thanthe first outer diameter D5. The second outer diameter D6 is the outerdiameter of the proximal shaft 502. In one example, the second outerdiameter D6 is 0.014 inch, but this is not meant to be limiting.

With an understanding of the components of catheter 500, it is nowpossible to describe the interactions of the various components and amethod to calculate a Fractional Flow Reserve (FFR). Referring back toFIGS. 9-10, a guide catheter (not shown but similar to FIG. 1) and theguidewire 516 are advanced through the vasculature to a desired site.The guidewire 516 may be back-loaded into the catheter 500 (i.e., theproximal end of the guidewire 516 is loaded into the distal end of theguidewire lumen 514 at the distal end of distal shaft 508). The catheter500 is in the first configuration with the movable shaft 542 disposedover the proximal shaft 502 and locked in place by the locking mechanismof the hub 526. The catheter 500 may then be advanced over the guidewire516 and through a lumen of the guide catheter to the desired treatmentsite. In particular, with a distal end of the guide catheter disposed ata desired site proximal of the stenosis 902, such as in the sinus of anaortic valve, the distal shaft 508 of the catheter 500 is advancedthrough the lumen of the guide catheter and distal of the distal end ofthe guide catheter. The catheter 500 is advanced such that distal shaft508 is disposed across the stenosis 902 of the vessel 900.

With the catheter 500 in position at the treatment site, the movableshaft 542 is removed from around the proximal shaft 502. Removing themovable shaft 542 results in the catheter 500 being in the secondconfiguration with only the proximal shaft 502 as the proximal portionof the catheter, as shown in FIGS. 10 and 11B. With the movable shaft542 removed, the combination of the guidewire 516 and the proximal shaft502 occupies a smaller percentage of the lumen of the guide catheter, asshown by comparing FIG. 11B to FIG. 11A. With the catheter 500 inposition and in the second configuration, the appropriate pressuremeasurements may be taken. Thus, blood flow adjacent the distal end ofthe guide catheter fills the lumen and tubing via a port in a proximalportion of the guide catheter. The proximal pressure P_(a) at the distalend of the guide catheter is measured by an external pressure transducervia the fluid (blood) column extending through the lumen of the guidecatheter and the tubing. Thus, an external pressure transducer isconfigured to measure the proximal or aortic (AO) pressure P_(a) at thedistal end of the guide catheter.

The external pressure transducer is configured to communicate themeasured proximal pressure P_(a) to a processor (not shown) via apressure transducer wire, as explained above with respect to thecatheter 100. However, this is not meant to limit the design and theexternal pressure transducer may communicate with the processor by anymeans suitable for the purposes described, including, but not limitedto, electrical cables, optical cables, or wireless devices.Simultaneously, the pressure sensor 518 measures distal pressure P_(d)of blood distal of the stenosis. The distal pressure P_(d) iscommunicated to the processor, as explained above. The processorcalculates the Fractional Flow Reserve (FFR) based on the distalpressure P_(d) divided by the proximal/aortic pressure P_(a), orFFR=P_(d)/P_(a).

As explained above, the proximal portion of the catheter 500 with themovable shaft 542 removed has a reduced cross-sectional profile (FIG.11B) as compared to the proximal portion of the catheter 500 with themovable shaft 542 disposed over the proximal shaft 502 (FIG. 11A). Asfurther explained above, because the proximal or aortic pressure P_(a)is measured using the fluid column within the lumen of the guidecatheter between an outer surface of a guidewire/proximal shaftcombination and an inner surface of the guide catheter, a larger profilemay lead to errors in the measured proximal or aortic pressure P_(a).Such errors are carried through to the FFR calculation noted abovebecause the measured proximal pressure P_(a) is used in the FFRcalculation. Thus, reducing the cross-sectional profile leads to asmaller potential for error in the proximal pressure P_(a), and hence asmaller potential for error in the FFR calculation.

Referring to FIGS. 12-14B, a catheter (or micro-catheter) 600 forcalculating a Fractional Flow Reserve (FFR) according to anotherembodiment of the present disclosure is shown. The catheter 600 includesa proximal shaft 602, a distal shaft 608, a pressure sensor 618, and atleast one pressure sensor wire 620, as shown in FIGS. 12-13. Thepressure sensor 618 and the at least one pressure sensor wire 620 aresimilar to the pressure sensor 118 and the at least one pressure sensorwire 120 of the catheter 100. Therefore, details of the pressure sensor618 and the at least one pressure sensor wire 620 will not be repeatedhere. The catheter 600 is configured to be disposed with a proximalportion of the proximal shaft 602 extending outside of a patient, and adistal portion of the distal shaft 608 positioned in situ within a lumen910 of a vessel 900 having a stenosis or lesion 902. The catheter 600 isconfigured such that the catheter 600 measures a distal pressure P_(d)of blood on a distal side 906 of the stenosis 902.

In an embodiment, the proximal shaft 602 of the catheter 600 is a hollowshaft including a proximal end 604 coupled a hub/handle 626, a distalend 606, and an inflation lumen 660 extending from the proximal end 604of the proximal shaft 602 to a distal portion 607 of the proximal shaft602. The distal portion 607 of the proximal shaft 602 is configured toextend through the stenosis 902 of the vessel 900 when the catheter 600is positioned for measuring the distal pressure P_(d). The distalportion 607 of the proximal shaft 602 is further configured to beradially expandable from a radially collapsed configuration (FIGS. 13and 14B) to a radially expanded configuration (FIGS. 12 and 14A). Thedistal portion 607 of the proximal shaft 602 has a first outer diameterD7 when in the radially expanded configuration (FIG. 14A) and a secondouter diameter D8 when in the radially collapsed configuration (FIG.14B), with the first diameter D7 being greater than the second diameterD8. In an embodiment, the distal portion 607 of the proximal shaft 602is formed of an elastic shape-memory material with a pre-set shape. Inthe embodiment of FIGS. 12-14B, the proximal shaft 602 has a pre-setshape in the radially collapsed configuration with the second outerdiameter D8, as shown in FIGS. 13 and 14B. Due to the shape memorymaterial and pre-set shape thereof, the distal portion 607 of theproximal shaft 602 of the catheter 600 actively recoils to the secondouter diameter D8 after removal of the inflation fluid from theinflation lumen 660. The expandable distal portion 607 of the proximalshaft 602 may be formed as described above with respect to the proximalshafts 102, 202 of the catheters 100, 200. For example, and not by wayof limitation, the distal portion 607 of the proximal shaft 602 may beformed as described in U.S. Pat. No. 9,192,751 to Macaulay et al., whichis incorporated by reference herein in its entirety. The distal portion607 of the proximal shaft 602 may be formed of material such as, but notlimited to, polyether block amide (PEBA, e.g. VESTAMID, PEBAX),thermoplastic elastomers (TPE), or other materials suitable for thepurposes described herein. The proximal shaft 602 may be coupled to thehub/handle 626 by adhesives, fusing, welding, or any other methodsuitable for the purposes of the present disclosure.

The inflation lumen 660 includes a proximal end 670 at a proximal end601 of the catheter 600 configured to be in fluid communication with aninflation fluid source (not shown). The inflation lumen 660 extendsthrough the proximal shaft 602 to a distal end 672 of the inflationlumen 660 in fluid communication with an interior cavity 609 of thedistal portion 607 of the proximal shaft 602, as shown in FIGS. 12-13.The distal portion 607 of the proximal shaft 602 is configured toradially expand when the interior cavity 609 of the distal portion isfilled with an inflation fluid, thereby transitioning to the radiallyexpanded configuration with the first outer diameter D7 (FIGS. 12 and14A). The distal portion 607 of the proximal shaft 602 is furtherconfigured such that as the pressure of the inflation fluid within theinterior cavity 609 is reduced, the outward radial force of theinflation fluid exerted on the inner surface of the distal portion 607decreases such that the distal portion 607 transitions to the radiallycollapsed configuration with the second outer diameter D8 (FIGS. 13 and14B). When the interior cavity 609 of the distal portion 607 of theproximal shaft 602 is filled with inflation fluid such that the distalportion is in the radially expanded configuration, strength andpushability of the distal portion 607 is increased as compared to whenthe inflation fluid is drained from the interior cavity 609. Thus, asdescribed in more detail below, the distal portion 607 is in theradially expanded configuration during delivery of the catheter 600 tothe desired treatment site.

In an embodiment, the distal shaft 608 of the catheter 600 includes aproximal end 610 and a distal end 612. A portion of the proximal end 610of the distal shaft 608 is coupled to a distal end 606 of the proximalshaft 602 by adhesives, fusing, welding, or any other method suitablefor the purposes of the present disclosure. The distal shaft 608 furtherincludes a guidewire lumen 614 configured to receive a guidewire 616therein, as shown in FIGS. 12-13. The distal shaft 608 further includesa proximal guidewire exit port 668 at a proximal portion 664 of thedistal shaft 608 configured to provide entry and exit of the guidewire616 to the guidewire lumen 614. The distal shaft 608 further includes adistal guidewire exit port at the distal end 612 of the distal shaft608. The distal shaft 608 further includes the pressure sensor 618 and adistal portion of the pressure sensor wire(s) 620. The distal portion ofthe pressure sensor wire(s) 620 may be disposed within a distal shaftwall 622 of the distal shaft 608. The distal shaft 608 is configured tobe disposed on the distal side 906 of the stenosis 902 such that thepressure sensor 618 is disposed on the distal side 906 of stenosis 902.

With an understanding of the components of the catheter 600 above, it isnow possible to describe the interactions of the various components anda method to calculate a Fractional Flow Reserve (FFR). Referring back toFIGS. 12-13, a guide catheter (not shown but as described above withrespect to FIGS. 1-2) and the guidewire 616 are advanced through thevasculature to a desired site. The guidewire 616 may be back-loaded intothe catheter 600 (i.e., the proximal end of the guidewire 616 is loadedinto the distal end of the guidewire lumen 614 at the distal end 612 ofthe distal shaft 608). The catheter 600 is in the radially expandedconfiguration with the distal portion 607 of the proximal shaft 602inflated. The catheter 600 may then be advanced over the guidewire 616and through a lumen of the guide catheter to the desired treatment site.In particular, with a distal end of the guide catheter disposed at adesired site proximal of the stenosis 902, such as in the sinus of anaortic valve, the catheter 600 is advanced through the lumen of theguide catheter until the distal shaft 608 is distal of the distal end ofthe guide catheter and on the distal side 906 of the stenosis 902, asshown in FIG. 12.

With the catheter 600 in position at the treatment site, the inflationfluid is drained from the interior cavity 609 of the distal portion 607of the proximal shaft 602. Thus, the distal portion 607 of the proximalshaft 602 returns to the radially collapsed configuration shown in FIGS.13 and 14B. With the distal portion 607 of the proximal shaft 602 in theradially collapsed configuration, the combination of the guidewire 616and the distal portion 607 occupies a smaller percentage of the vessel900 through the stenosis 902, as shown by comparing FIG. 14B to FIG.14A. With the catheter 600 in position and in the radially collapsedconfiguration, the appropriate pressure measurements may be taken. Thus,blood flow adjacent the distal end of the guide catheter fills the lumenand tubing via a port in a proximal portion of the guide catheter. Theblood pressure P_(a) at the distal end of the guide catheter is measuredby an external pressure transducer via the fluid (blood) columnextending through the lumen of the guide catheter and the tubing. Thus,an external pressure transducer is configured to measure proximal oraortic (AO) pressure P_(a) at the distal end of the guide catheter.

The external pressure transducer is configured to communicate measuredproximal pressure P_(a) to a processor (not shown) via a pressuretransducer wire, as explained above with respect to the catheter 100.However, this is not meant to limit the design and the external pressuretransducer may communicate with the processor by any means suitable forthe purposes described, including, but not limited to, electricalcables, optical cables, or wireless devices. Simultaneously, thepressure sensor 618 measures distal pressure P_(d) of blood distal ofthe stenosis. The distal pressure P_(d) is communicated to theprocessor, as explained above. The processor calculates the FractionalFlow Reserve (FFR) based on the distal pressure P_(d) divided by theproximal/aortic pressure P_(a), or FFR=P_(d)/P_(a).

As explained in the Background Section above, an FFR catheter with aguidewire extending therethrough occupies a larger percentage of thevessel 900 through the stenosis 902 than a conventional FFR wire. Thisdisrupts the blood flow through the stenosis, which can lead to ameasured distal pressure P_(d) which does not correlate to a distalpressure measured distal of the same stenosis with an FFR wire. Further,the FFR catheter needs sufficient pushability to be delivered throughthe vasculature to the treatment site, which may increase the size ofsuch FFR catheters. In the embodiment of FIGS. 12-14B, the distalportion 607 of the proximal shaft 602 is inflated during delivery of thecatheter 600 to the treatment site to provide sufficient pushability.Once at the treatment site, the distal portion 607 may be deflated suchthat the overall cross-sectional profile of the guidewire 616 and distalportion 607 in the radially collapsed configuration is equivalent to thecross-sectional profile of an FFR wire. Thus, the measured distalpressure P_(d) is equivalent to the measured distal pressure using anFFR wire.

Referring to FIGS. 15-17B, a catheter (or micro-catheter) 700 forcalculating a Fractional Flow Reserve (FFR) according to anotherembodiment of the present disclosure is shown. The catheter 700 includesa proximal shaft 702, a distal shaft 708, a pressure sensor 718, and atleast one pressure sensor wire 720. The distal shaft 708, pressuresensor 718 and the at least one pressure sensor wire 720 are similar tothe distal shaft 608, pressure sensor 118 and the at least one pressuresensor wire 120 described above with respect to the catheter 600(regarding the distal shaft) and the catheter 100 (regarding thepressure sensor and the pressure sensor wire(s)). Therefore, details ofthe distal shaft 708, the pressure sensor 718, and the at least onepressure sensor wire 720 will not be repeated here. The catheter 700 isconfigured to be disposed with a proximal portion of the proximal shaft702 extending outside of a patient, and a distal portion of the distalshaft 708 positioned in situ within a lumen 910 of a vessel 900 having astenosis or lesion 902. The catheter 700 is configured to measure adistal pressure P_(d) of blood on a distal side 906 of the stenosis 902.

The proximal shaft 702 is disposed distal of and coupled to a hub 726 byadhesives, fusing, welding, or any other method suitable for thepurposes of the present disclosure. Proximal shaft 702 is a hollow shafthaving a proximal end 704, and distal end 706, and an interior cavity760. Proximal shaft 702 may be formed of an elastic shape-memorymaterial with a pre-set shape such that proximal shaft 702 is radiallyexpandable from a radially collapsed configuration (FIGS. 16 and 17B) toa radially expanded configuration (FIGS. 15 and 17A). The proximal shaft702 has a first diameter D9 when in the radially expanded configurationand a second diameter D10 when in the radially collapsed configuration,with the first diameter D9 being greater than the second diameter D10,as shown in FIGS. 17A-17B. In the embodiment of FIGS. 15-17B, theproximal shaft 702 has a pre-set shape in a radially collapsedconfiguration with the second diameter D10, as shown in FIGS. 16 and17B. Due to the shape memory material and pre-set shape thereof, theproximal shaft 702 actively recoils to the radially collapsedconfiguration upon removal of inflation fluid from the inflationinterior cavity 760. The expandable proximal shaft 702 may be formed asdescribed above with respect to the proximal shafts 102, 202 of thecatheters 100, 200. For example, and not by way of limitation, theproximal shaft 702 may be formed as described in U.S. Pat. No. 9,192,751to Macaulay et al., which is incorporated by reference herein in itsentirety. The proximal shaft 702 may be formed of, for example, and notby way of limitation, polyether block amide (PEBA, e.g. VESTAMID,PEBAX), thermoplastic elastomers (TPE), or other materials suitable forthe purposes described herein.

The interior cavity 760 includes a proximal end 770 in fluidcommunication with an inflation fluid source (not shown) through aninflation lumen 762 disposed through the hub 726. The interior cavity760 also includes a distal end 772 adjacent a location where theproximal shaft 702 is coupled to the distal shaft 708. The proximalshaft 702 is configured such that the inflation fluid, pumped underpressure into the interior cavity 760, fills the interior cavity 760 andexerts an outward radial force on an inner surface of the proximal shaft702 such that the proximal shaft 702 transitions to the radiallyexpanded configuration (FIGS. 15 and 17A). The proximal shaft 702 isfurther configured such that as the pressure of the inflation fluidwithin the interior cavity 760 is reduced, the outward radial force ofthe inflation fluid exerted on the inner surface of the proximal shaft702 decreases such that the proximal shaft 702 transitions to theradially collapsed configuration (FIGS. 16 and 17B). The proximal shaft702 with interior cavity 760 filled with inflation fluid under pressure(i.e., the radially expanded configuration) has sufficient strength andpushability for delivery of the catheter 700 to the desired treatmentsite.

With an understanding of the components of the catheter 700 above, it isnow possible to describe the interactions of the various components anda method to calculate a Fractional Flow Reserve (FFR). Referring back toFIGS. 15-16, a guide catheter (not shown but as described above withrespect to FIGS. 1-2) and the guidewire 716 are advanced through thevasculature to a desired site. The guidewire 716 may be back-loaded intothe catheter 700 (i.e., the proximal end of the guidewire 716 is loadedinto the distal end of the guidewire lumen 714 at the distal end 712 ofthe distal shaft 708). The catheter 700 is in the radially expandedconfiguration with the proximal shaft 702 inflated with inflation fluid.The catheter 700 may then be advanced over the guidewire 716 and througha lumen of the guide catheter to the desired treatment site. Inparticular, with a distal end of the guide catheter disposed at adesired site proximal of the stenosis 902, such as in the sinus of anaortic valve, the catheter 700 is advanced through the lumen of theguide catheter until the distal shaft 708 is distal of the distal end ofthe guide catheter and on the distal side 906 of the stenosis 902, asshown in FIG. 15.

With the catheter 700 in position at the treatment site, the inflationfluid is drained from the interior cavity 760 of the proximal shaft 702.Thus, the proximal shaft 702 returns to the radially collapsedconfiguration shown in FIGS. 16 and 17B. With the catheter 700 inposition and the proximal shaft 702 in the radially collapsedconfiguration, the appropriate pressure measurements may be taken. Thus,blood flow adjacent the distal end of the guide catheter fills the lumenof the guide catheter to an external transducer via tubing and a port ina proximal portion of the guide catheter. The blood pressure P_(a) atthe distal end of the guide catheter is measured by the externalpressure transducer via the fluid (blood) column extending through thelumen of the guide catheter and the tubing. Thus, the external pressuretransducer is configured to measure the proximal or aortic (AO) pressureP_(a) at the distal end of the guide catheter.

The external pressure transducer is configured to communicate measuredproximal pressure P_(a) to a processor (not shown) via a pressuretransducer wire, as explained above with respect to the catheter 100.However, this is not meant to limit the design and the external pressuretransducer may communicate with the processor by any means suitable forthe purposes described, including, but not limited to, electricalcables, optical cables, or wireless devices. Simultaneously, thepressure sensor 718 measures distal pressure P_(d) of blood distal ofthe stenosis. The distal pressure P_(d) is communicated to theprocessor, as explained above. The processor calculates the FractionalFlow Reserve (FFR) based on the distal pressure P_(d) divided by theproximal/aortic pressure P_(a), or FFR=P_(d)/P_(a).

As explained in the Background Section above, an FFR catheter with aguidewire extending therethrough occupies a larger percentage of thevessel 900 through the stenosis 902 than a conventional FFR wire. Thisdisrupts the blood flow through the stenosis, which can lead to ameasured distal pressure P_(d) which does not correlate to a distalpressure measured distal of the same stenosis with an FFR wire.Similarly, a proximal portion of an FFR catheter with a guidewiredisposed therein occupies a larger percentage of the lumen of the guidecatheter, thereby possibly causing the measured proximal pressure P_(a)to not correlate to a proximal pressure measured by an FFR wire.However, with the proximal shaft 702 in the radially collapsedconfiguration, the cross-sectional profile of the distal portion 707 ofthe proximal shaft 702 disposed through the stenosis 902 is negligible.Thus, the combined cross-sectional profile of the guidewire 716 and thedistal portion 707 of the proximal shaft is equivalent to an FFR wirealone passing through the stenosis 902. Further, the cross-sectional ofthe proximal portion of the proximal shaft 702 extending through thelumen of the guide catheter occupies is also negligible. Thus, thecross-sectional profile if the guidewire 716 and the proximal portion ofthe proximal shaft 702 extending through the guide catheter isequivalent to the cross-sectional profile of an FFR wire. Therefore, FFRmeasured with the catheter 700 with the proximal shaft in the radiallycollapsed configuration is equivalent to the FFR measured with an FFRwire, thereby alleviating the need for a correction factor.

Referring to FIGS. 18-20B, a catheter (or micro-catheter) 800 forcalculating a Fractional Flow Reserve (FFR) according to anotherembodiment of the present disclosure is shown. The catheter 800 includesa proximal shaft 802, a distal shaft 808, a pressure sensor 818, and atleast one pressure sensor wire 820. The pressure sensor 818 and the atleast one pressure sensor wire 820 are similar to the pressure sensor118, and the at least one pressure sensor wire 120 described above withrespect to the catheter 100. Therefore, details of the pressure sensor818 and the at least one pressure sensor wire 820 will not be repeatedhere. The catheter 800 is configured to be disposed with a proximalportion of the proximal shaft 802 extending outside of a patient and adistal portion of the distal shaft 808 positioned in situ within a lumen910 of a vessel 900 having a stenosis or lesion 902. The catheter 800 isconfigured to measure a distal pressure P_(d) of blood on a distal side906 of the stenosis 902.

In an embodiment, the proximal shaft 802 of the catheter 800 may be ahollow shaft with the pressure sensor wires(s) 820 extending through alumen of the proximal shaft 802. In other embodiment, the proximal shaft822 may be a solid core wire with the pressure sensor wire(s) attachedto an outer surface thereof. The proximal shaft 802 includes a proximalend coupled to a handle or hub 826 and a distal end 806 coupled to thedistal shaft 808. The proximal shaft 802 is configured to providesufficient stability and pushability to advance catheter 800 to thedesired treatment site.

In an embodiment, the distal shaft 808 of the catheter 800 includes aproximal end 810 coupled to the distal end 806 of the proximal shaft802, and a distal end 812 defining a distal end of the catheter 800. Asshown in FIGS. 18-19, the distal shaft 808 may be described as includinga proximal or guidewire receiving portion 811, an expandable portion809, and a distal or sensor portion 813. A guidewire lumen 814 isdefined within the distal shaft 808. The guidewire lumen 814 extendsdistally from a guidewire port 868 in the proximal portion 811 of thedistal shaft 808 to a guidewire exit port 813 at the distal end of thedistal shaft 808. The guidewire lumen 814 is configured to accept adistal portion of the guidewire 816 therein, as shown in FIG. 18. Thedistal shaft 808 further includes the pressure sensor 818 and a distalportion of the pressure sensor wire(s) 820 disposed within a distalshaft wall 822. The distal shaft 808 is configured to be disposed on thedistal side 906 of the stenosis 902 such that the pressure sensor 818 isdisposed on the distal side 906 of stenosis 902. The distal shaft 808may be coupled to the proximal shaft 802 by, for example, and not by wayof limitation, adhesives, fusing, welding, for any other method suitablefor the purposes of the present disclosure.

The expandable portion 809 of the distal shaft 808 is configured toextend through the stenosis 902 of the vessel 900 when the catheter 800is positioned for measuring the distal pressure P_(d) on a distal side906 of the stenosis 902. The expandable portion 809 is expandable andcollapsible such that the expandable portion 809 includes a radiallyexpanded configuration (FIGS. 18 and 20A) and a radially collapsedconfiguration (FIGS. 19 and 20B). The expandable portion 809 has a firstdiameter D11 when in the radially expanded configuration and a seconddiameter D12 when in the radially collapsed configuration, with thefirst diameter D11 being greater than the second diameter D11, as shownin FIGS. 20A-20B. The expandable portion 809 is formed of an elasticshape-memory material with a pre-set shape. In the embodiment of FIGS.18-20B, the expandable portion 809 has a pre-set shape in the radiallycollapsed configuration with the second diameter D12, as shown in FIGS.19 and 20B. Due to the shape memory material and pre-set shape thereof,the expandable portion 809 actively recoils to the second diameter D12upon removal of the guidewire 816 from the guidewire lumen 814. Theexpandable portion 809 may be formed as described above with respect tothe proximal shafts 102, 202 of the catheters 100, 200. For example, andnot by way of limitation, the expandable portion 809 may be formed asdescribed in U.S. Pat. No. 9,192,751 to Macaulay et al., which isincorporated by reference herein in its entirety.

In the embodiment of FIGS. 18-20B, the guidewire 816 provides stabilityto the expandable portion 809 during delivery of the catheter 800 to thetreatment site. Because the expandable portion 809 is near the distalend 812 of the catheter 800, less pushability is required than near theproximal end of the catheter 800. The guidewire 816 is configured to bemovable within the guidewire lumen 814 of the catheter 800 as shown inFIGS. 18-19. Upon retraction of the guidewire 814 from the expandableportion 809, as shown in FIG. 19, the expandable portion 809 of theproximal shaft 802 collapses to the radially collapsed configuration, aspreviously described.

With an understanding of the components of the catheter 800 above, it isnow possible to describe the interactions of the various components anda method to calculate a Fractional Flow Reserve (FFR). Referring back toFIGS. 18-19, a guide catheter (not shown but as described above withrespect to FIGS. 1-2) and the guidewire 816 are advanced through thevasculature to a desired site. The guidewire 816 may be back-loaded intothe catheter 800 (i.e., the proximal end of the guidewire 816 is loadedinto the guidewire exit port 813 at the distal end of the guidewirelumen 814). As the catheter 800 is advanced over the guidewire 816, theguidewire 816 expands the expandable portion 809 to the radiallyexpanded configuration. As the catheter 800 continues to advance overthe guidewire 816, the guidewire exits the catheter 800 throughguidewire port 868 proximal of the expandable portion 809. The catheter800 is advanced over the guidewire 816 and through a lumen of the guidecatheter to the desired treatment site. In particular, with a distal endof the guide catheter disposed at a desired site proximal of thestenosis 902, such as in the sinus of an aortic valve, the catheter 800is advanced through the lumen of the guide catheter until the distalshaft 808 is distal of the distal end of the guide catheter such thatthe expandable portion 809 traverses the stenosis 902 and the pressuresensor 818 is on the distal side 906 of the stenosis 902, as shown inFIG. 18.

With the catheter 800 in position at the treatment site, the guidewire816 is retracted proximally such that the guidewire 816 is proximal ofthe expandable portion 809 but still disposed within the guidewire lumen814, as shown in FIG. 19. Essentially, a distal end of the guidewire 816is disposed within the guidewire lumen 814 between the guidewire port868 and the expandable portion 809, as shown in FIG. 19. Retraction ofthe guidewire from the guidewire lumen 814 of the expandable portion 809causes the expandable portion 809 to radially collapse to the radiallycollapsed configuration shown in FIGS. 19 and 20B. With the catheter 800in position and expandable portion 809 in the radially collapsedconfiguration, the appropriate pressure measurements may be taken. Thus,blood flow adjacent the distal end of the guide catheter fills the lumenof the guide catheter to an external transducer via tubing and a port ina proximal portion of the guide catheter. The blood pressure P_(a) atthe distal end of the guide catheter is measured by the externalpressure transducer via the fluid (blood) column extending through thelumen of the guide catheter and the tubing. Thus, the external pressuretransducer is configured to measure proximal, or aortic (AO) pressureP_(a) at the distal end of the guide catheter.

The external pressure transducer is configured to communicate measuredproximal pressure P_(a) to a processor (not shown) via a pressuretransducer wire, as explained above with respect to the catheter 100.However, this is not meant to limit the design and the external pressuretransducer may communicate with the processor by any means suitable forthe purposes described, including, but not limited to, electricalcables, optical cables, or wireless devices. Simultaneously, thepressure sensor 818 measures distal pressure P_(d) of blood distal ofthe stenosis. The distal pressure P_(d) is communicated to theprocessor, as explained above. The processor calculates the FractionalFlow Reserve (FFR) based on the distal pressure P_(d) divided by theproximal/aortic pressure P_(a), or FFR=P_(d)/P_(a).

As explained in the Background Section above, an FFR catheter with aguidewire extending therethrough occupies a larger percentage of thevessel 900 through the stenosis 902 than a conventional FFR wire. Thisdisrupts the blood flow through the stenosis, which can lead to ameasured distal pressure P_(d) which does not correlate to a distalpressure measured distal of the same stenosis with an FFR wire. In theembodiment of FIGS. 18-20B, with the expandable portion 809 in theradially collapsed configuration, the cross-sectional profile of thecollapsible portion 809 disposed through the stenosis 902 is equivalentto the cross-sectional profile of an FFR wire. For example, and not byway of limitation, the second diameter D12 may be approximately 0.014inch. Therefore, because the cross-sectional profile of the expandableportion 809 is similar to the cross-sectional profile of an FFR wirecrossing the stenosis 902, the measured distal pressure P_(d) isequivalent to the measured distal pressure using an FFR wire. Therefore,the FFR calculated using measurements taken with the catheter 800 withthe expandable portion 809 in the radially collapsed configuration isequivalent to the FFR calculated using measurements taken with an FFRwire, thereby alleviating the need for a correction factor.

While only some embodiments according to the present invention have beendescribed herein, it should be understood that they have been presentedby way of illustration and example only, and not limitation. Variouschanges in form and detail can be made therein without departing fromthe spirit and scope of the invention. Further, each feature of eachembodiment discussed herein, and of each reference cited herein, can beused in combination with the features of any other embodiment. Forexample, and not by way of limitation, the embodiments describing aradially expandable/collapsible proximal shaft may be combined with theembodiments describing a radially expandable/collapsible distal shaft.All patents and publications discussed herein are incorporated byreference herein in their entirety.

What is claimed is:
 1. A catheter for measuring a fractional flowreserve, the catheter comprising: a proximal shaft, wherein at least aproximal portion of the proximal shaft adjacent a hub of the cathetercoupled to a proximal end of the proximal shaft includes a radiallyexpanded configuration and a radially collapsed configuration, whereinat least the proximal portion of the proximal shaft has a first outerdiameter in the radially expanded configuration and a second outerdiameter in the radially collapsed configuration, wherein the firstouter diameter is larger than the second outer diameter; a distal shaftcoupled to the proximal shaft, the distal shaft defining a guidewirelumen configured to receive a guidewire therein, wherein at least aportion of the distal shaft is not collapsible; and a pressure sensorcoupled to the distal shaft.
 2. The catheter of claim 1, furthercomprising a stiffening shaft movable within an expansion lumen of theproximal shaft, wherein the proximal shaft is in the radially expandedconfiguration with the stiffening shaft disposed in the expansion lumen,and wherein the proximal shaft is in the radially collapsedconfiguration with the stiffening shaft removed from the expansionlumen.
 3. The catheter of claim 2, wherein the proximal shaft is formedof a shape memory material including a pre-set shape.
 4. The catheter ofclaim 3, wherein the pre-set shape of the proximal shaft is the radiallycollapsed configuration, and wherein the proximal shaft is expanded tothe radially expanded configuration by the stiffening shaft.
 5. Thecatheter of claim 4, wherein the proximal shaft comprises an extrudedelastic material such that in the radially collapsed configuration theextruded elastic material collapses the expansion lumen, and wherein thestiffening shaft extending through the expansion lumen expands theexpansion lumen such that the proximal shaft is in the radially expandedconfiguration.
 6. The catheter of claim 4, wherein the proximal shaftcomprises a circumferentially continuous material layer, an elasticframe, and a partially non-circumferentially continuous material layerconnected to the elastic frame and surrounding the circumferentiallycontinuous material layer, the partially non-circumferentiallycontinuous material layer having a gap, wherein in the radiallycollapsed configuration the gap has a first circumferential length, andwherein in the radially expanded configuration the gap has a secondcircumferential length larger than the first circumferential length. 7.The catheter of claim 6, wherein the circumferentially continuous layerincludes a fold in the collapsed configuration, and wherein thecircumferentially continuous layer unfolds to expand to the radiallyexpanded configuration.
 8. The catheter of claim 1, further comprisingat least one pressure sensor wire operably connected to the pressuresensor, wherein the at least one pressure sensor wire extends proximallyfrom the pressure sensor within a distal shaft wall and extendsproximally into a proximal shaft wall of the proximal shaft.
 9. A methodfor calculating a Fractional Flow Reserve in a vessel, the methodcomprising the steps of: delivering a catheter to a treatment site inthe vessel, the catheter including a pressure sensor coupled to a distalshaft, a proximal shaft including a proximal end coupled to a hub, and astiffening shaft disposed within an expansion lumen of the proximalshaft disposed at least adjacent to a proximal portion of the proximalshaft adjacent the hub, wherein the catheter is delivered to thetreatment site with the stiffening shaft disposed in the expansion lumenand such that the pressure sensor is located on a distal side of astenosis of the vessel; removing the stiffening shaft from the expansionlumen such that at least the proximal portion of the proximal shaftcollapses from a radially expanded configuration to a radially collapsedconfiguration, wherein at least a portion of the distal shaft does notcollapse; measuring a distal pressure distal of the stenosis using thepressure sensor; measuring a proximal pressure on a proximal side of thestenosis, wherein the proximal pressure is measured with the proximalshaft in the radially collapsed configuration; calculating theFractional Flow Reserve using the measured distal pressure and themeasured proximal pressure.